The invention relates to a film deposition device for depositing a protective film or a functional film on a surface of a film material such as a film and sheet, or a solid material such as a magnetic head.
Heretofore, in order to control a thickness of a film deposited by a film deposition device and stop the device at appropriate time, a time control or in-situ film thickness monitoring control has been carried out. In the time control, it is assumed that a film thickness is proportional to film deposition time. The film thickness and the film deposition time are measured beforehand, and a film deposition speed per unit time is calculated. The film deposition is stopped manually or automatically at time when a desired thickness is obtained based on the data obtained described above. In the in-situ film thickness monitoring control, a thickness is measured at real time by using a quartz oscillator type film thickness monitor, an Ellipsometer type film thickness monitor and the like. The film deposition is stopped manually or automatically at time when a desired thickness is obtained.
Hereunder, a structure and an operation of a conventional in-situ film thickness monitoring control will be explained with reference to FIG. 7. Reference numeral 1 represents a plasma source, wherein a filtered catholic vacuum arc (hereinafter referred to as FCVA) using arc discharge has been practically used (refer to Shimadzu Corporation catalog C676-0091, ‘Filtered Catholic Vacuum Arc (FCVA)’). A plasma CVD using high frequency discharge in a magnetic field has also been used practically.
In the plasma source 1, a plasma flow 3, i.e. a mixture of electrons having negative charges and positive ions of a material of a film, is generated. A guiding path 2 is provided for guiding the plasma flow 3 into a depositing chamber 6. Generally, the guiding path 2 is formed of a mechanical electromagnetic filter for removing neutral particles other than plasma (refer to Shimadzu Corporation catalog C676-0091, ‘Filtered Catholic Vacuum Arc (FCVA)’). In the depositing chamber 6, there are disposed a shutter 5 fixed to a shutter shaft 4, a monitoring sensor 7, a substrate holder 9 and a substrate 10 detachably attached to the substrate holder 9. The shutter shaft 4 is rotated by a motor M to open and close the shutter 5. FIG. 7 shows a state where the shutter 5 is opened. The positive ions in the plasma are accumulated on the substrate 10 to deposit a film. A part of the positive ions is accumulated on the monitoring sensor 7. The monitoring sensor 7 is a quartz oscillator type film thickness monitoring sensor. An accumulated weight of the material on the monitoring sensor 7 changes an oscillation frequency of the quartz oscillator, and an electric signal is sent to a control power source 11 through a transmission line 8. The control power source 11 displays the change in the oscillation frequency of the quartz oscillator, and a film deposition completion signal is sent when the oscillation frequency reaches a predetermined value.
Under an assumption that the accumulated weight of the material on the monitoring sensor 7 is proportional to a thickness of the film deposited on the substrate 10, a relationship between the thickness and the change in the oscillation frequency is obtained beforehand as calibration data. Accordingly, it is possible to send the completion signal from the control source 11 at proper time. A thickness of the film deposited on the substrate 10 is separately measured by a commercially available mechanical film thickness meter or an Ellipsometer (described later) to obtain the calibration data as described above.
Incidentally, as another method for measuring a film thickness, an in-situ spectro-Ellipsometer may be used (refer to J. A. Woollam, Japan-Research and Instrumentation —Technical Report— ‘Analysis Method of Ellipsometer Data’). In this case, an optical beam is incident on the substrate 10 during the film deposition through an optical window (not shown) from outside of the depositing chamber 6. Light reflected from a film deposition surface is guided outside of the depositing chamber 6 and incident on a sensor (not shown) of Ellipsometer, so that a polarized state of the reflected light is analyzed to calculate a film thickness. There has been also developed another type of Ellipsometer, wherein a combination of an optical beam illuminator and a sensor using a vacuum-resist type optical fiber is introduced in the depositing chamber 6, and light is incident on the substrate 10 without using the vacuum window to measure a film thickness. In the present specification, such a quartz oscillator type film thickness monitoring sensor is explained.
Before a film is deposited, the calibration data is obtained in a preparation process. In the film deposition process, first, the plasma source 1, the guiding path 2 and the depositing chamber 6 are evacuated by a vacuum pump (not shown) to a predetermined vacuum rate. A predetermined gas or particles (not shown) as a raw material of the film are supplied to the plasma source 1 to continue the discharge, and the plasma starts generating in a state that the shutter 5 is closed. Next, the shutter 5 is opened to flow the plasma flow 3 against the substrate 10 so that the positive ions of the material are accumulated on the substrate 10. When a predetermined film thickness according to the calibration data is obtained, the deposition completion signal is sent from the control power source 11 to the motor M to rotate the shutter shaft 4, so that the shutter 5 is closed to thereby complete the film deposition.
Incidentally, a property of the film deposited on the substrate 10 is influenced by a potential of the substrate 10. Accordingly, a potential from an outer power source (not shown) is supplied to the substrate 10 as needed. For example, when the substrate 10 is held at a negative potential, it is possible to control a quantity of the electrons entering the substrate 10 together with the positive ions of the material.
As shown in FIG. 8, a further conventional film deposition device has been proposed, wherein the plasma flow 3 is deposited in a beam shape through the guiding path 2 with a specific shape or an electromagnetic device (not shown). A scanner SU is provided in the vicinity of an incident position of the plasma flow 3 entering the depositing chamber 6, so that the plasma flow 3 is scanned in a vertical direction and in a direction perpendicular to a surface of the drawing. Hereinafter, such a device is referred to as a scanning type film deposition device. In this case, the plasma beam at certain time is oriented in only one direction, such as a direction of the monitoring sensor 7 or a direction of the substrate 10, so that a specific point is irradiated every cycle determined by a setting condition of the scanner SU.
Therefore, the oscillation frequency of the monitoring sensor 7 is changed in a step pattern at every cycle, and the electrical signal is sent to the control power source 11 through the transmission line 8. In FIG. 8, the structural elements and operation except the guiding path 2 and the scanner SU are basically the same as those shown in FIG. 7, so that explanations thereof are omitted. Also, in FIG. 8, the shutter shaft 4, the shutter 5 and the motor M shown in FIG. 7 are omitted.
The conventional film deposition devices have the structures described above. In the structures, a control area and control accuracy of the film thickness are not sufficient. In other words, a quantity of the plasma generated by the plasma source is fluctuated with time due to variations in gas flow quantity, discharge intensity and the like. However, in the time control, there is no function to follow the fluctuation, i.e. a change in the film deposition rate, in real time, thereby making it difficult to constantly control the film thickness. In the quartz oscillator type film thickness monitor, the weight change of the material is monitored as the frequency change. The frequency change is generally not large enough for measuring a thin film having a thickness less than 100 nm. Accordingly, when a protective film having a thickness of, for example, 2 to 3 nm, is formed on a magnetic head, it is difficult to use the method.
The Ellipsometer is suitable for measuring a film thickness in the atmosphere without any time restriction and has a high accuracy. However, it is necessary to take time for analysis to measure the polarization quantity and calculate a thickness. Even if the in-situ spectro-Ellipsometer type film thickness monitor is used, the analysis requires time in the order of a few seconds and the measurement becomes discrete. Accordingly, it is difficult to measure a film thickness increasing at a high speed at real time and immediately close the shutter 5. Further, it is necessary to perform smoothing calculations based on the data several times and output the film deposition completion signal based on estimated completion time. In particular, when a film has a thickness less than several tens of nm, the film deposition time becomes shorter than the analysis time, so that it is very difficult to accurately control a film thickness. Therefore, in order to apply the method with high precision, it is necessary to reduce the film deposition rate to an extremely small rate, or interrupt the film deposition several times to measure a film thickness repeatedly, thereby making the process complicated and lowering throughput.
In the conventional structure, the monitoring sensor 7 monitors the accumulated quantity of the material. Accordingly, when an intensity of the plasma flow 3 is significantly fluctuated with time or the plasma flow 3 has a fluctuated distribution with time, the correlation between the accumulated quantity to be monitored and a thickness of a film deposited on the substrate 10 is not always sufficient. That is, in the film deposition device shown in FIG. 8, when the flow rate of the plasma is fluctuated with time, since the plasma flow beam does not irradiate the monitoring sensor 7 at the same time when the plasma flow beam irradiates the substrate 10, an output of the monitoring sensor 7 does not correctly reflect the plasma quantity on the substrate 10, thereby shifting the correlation.
Also, the plasma flow beam irradiates the monitoring sensor 7 in an extremely short period of time as compared with the film deposition time. Accordingly, the accumulated quantity of the material irradiating the monitoring sensor at certain time is small and influenced by a noise. Further, in the system shown in FIG. 7, when a distribution of the plasma flow 3 entering the depositing chamber 6 through the guiding path 2 is fluctuated with time, the correlation between the output of the monitoring sensor 7 and a thickness of a film deposited on the substrate 10 is impaired, thereby making it difficult to accurately control a film thickness.
In view of the problems described above, an object of the present invention is to provide a film deposition device for accurately controlling a film thickness.
Further objects and advantages of the invention will be apparent from the following description of the invention.